Changes

This article works through the considerations in designing heating, ventilation and air-conditioning (HVAC) systems for year-round living on a 50-foot boat. Some of the concepts and calculations can also be applied to your next house.

The HVAC system uses a blend of loosely coupled systems to provide maximum energy efficiency and redundancy for a year-round live-aboard. Fresh-air ventilation uses small zone-based air vents but this makes humidity control difficult. The heating and cooling systems use a shared circulating-water distribution system to minimise bulkhead pass-throughs. Heating design is by a diesel furnace with backup from a diesel fireplacenot optimal. Cooling is by a chiller with keel cooler, with backup from When the cold-plate refrigeration system. Hot water furnace fails in the coldest weather there is heated by the engine, the diesel oven, a solar collector or AC elements using shore power or the house bank. The provided calculator gives heating and air conditioning requirements in shortfall of 21,560 BTU/hor 6 kilowatts (kW).

A basic heating, ventilation and air conditioning system is described below. In this case the The design goal is a year-round live-aboard in north-eastern North America. For completeness in understanding the trade-offs made, the engine cooling system, hot water and refrigeration and watermaker are also shown. Some of the design considerations are:

The requirement for a single fuel type effectively eliminates propane heating in favour of diesel. Diesel is anyway much safer. It is also more efficient, providing around 140,000 BTU (British Thermal Units) per gallon(gal), compared to 91,000 for propane.

The first major issue is whether to use forced air or circulating water to distribute heating and cooling. In the beginning, memories Memories of cold radiators in grade school in the dead of a Canadian winter, and the comfort of humidity control with forced air in modern homes predisposed me the solution to forced air. Over time, I the solution changed my mind several times. In the end, circulating water was chosen to:

== Heating ==Methods of calculating requirements for both heating and air conditioning tend In addition, to provide backup in the arcane case of failure in a severe cold spell, a diesel bulkhead fireplace in the salon, such as the Kabola <ref>http://www.kabola.nl/</ref> Old English Diesel Room Heater or the very simplisticHarworth Bubble <ref>http://www. There are too many variables to consider, ebubbleproducts.gco., uk/</ref> is also plumbed into the colour distribution system. Other types of the deck paint affects the amount of heat gain insidebulkhead heater are available from Dickinson Marine <ref>http://dickinsonmarine. The author has developed a spreadsheet application that tries to strike a balance between simplicity com/</ref>, Refleks <ref>http://www.refleks-olieovne.dk/</ref> and accuracySigmar <ref>http://www. When calculating heating requirementssigmarine.com/</ref>.Initially a fireplace was desired for lifestyle reasons, but as the design evolved it ignores heat gain through southern exposure windows became a backup system. The Dickinson Bristol Diesel Cook Stove in the daytime and heat loss through all windows at night. It galley can also ignores sporadic heat gain from equipment and appliancesthe forward accommodation, but it is not part of the main distribution system.

V = volume of the accommodation in cubic metres== Engine Cooling ===

T = Under way, engine coolant circulates through the hot water tank, and hence to a water-water heat exchanger with keel cooler. Another feature of this design is that raw seawater is not circulated through the engine. There is a bypass circuit around the water heater that closes thermostatically when the heater is at temperature differential in degrees Celsius.

K = dispersion coefficient (how heat ‘lossy’ is your In winter if the boat)is out of the water, the engine may have to be run to charge the batteries. In this case, an optional water-air radiator in the engine room provides engine cooling.

B = 4 == Hot Water ===Hot water is heated in several ways. In port in summer, the water is heated by standard electrical elements operating off the alternating current (conversion factor to BTUAC)system. In winter, it is heated by the water jacket on the diesel oven. If the oven is not in use, and there is no other source of heat, the hot water tank defaults to the electrical elements.

To calculate the VolumeUse an anti-scald, for each living space multiply Length * Width * Height in feet as shown in balanced-pressure shower valve (not a tempering valve!) on the below table. Use judgement in deciding whether showers to list each space individually or as part of a sectionregulate the water to 120 Fahrenheit (°F) 48.8 Celsius (°C). The calculator This will do avoid scalding people, and reduce water consumption. Bathers will be able to mix the conversion water faster to metrica comfortable temperature.

C = Additional cooling for one zone is provided by a cold-plate refrigeration system. A high-efficiency cold-plate design for the refrigeration will reduce AC loads, while not imposing a continuous direct current (F – 32DC) * 5/9load. Excess capacity may be used for air conditioning.

K = 3.0 - 4.0 (Simple construction, simple windows - Not insulated)= HVAC Scenarios ==

K = 2.0 - 2.9 (Simple constructionWith this integrated design, simple windows - Poorly insulated)the following scenarios apply:

Fresh air ventilation is required to replenish oxygen removed by people and sources of combustion, and to dilute odours and pollutants. Local exhaust ventilation is required Main engine in heads and the galley to remove airborne odours before they spread through the boat. From a ventilation viewpoint, the most effective method is an integrated HVAC system with air distribution and local controls in each cabin. Such a system can include an air-to-air heat exchanger to precondition the temperature of the air and recover energy, and a humidifier/dehumidifier to control levels of indoor moisture. Humidity control is especially important in hot humid climates where unconditioned ventilation can deliver 1-lb of water per cubic foot of intake air.use:

Excess humidity causes condensation on windows and Central hot water pipes. It can blister paint, rust metal and warp wood, and cause electrical faults. Dust mites, fungus, mildew and mould thrive in humid conditions, aggravating allergies and sometimes damaging lungs. Insects like clothes moths, cockroaches and fleas also like high humidity.AC is turned off

Unfortunately I decided against an air distribution system in favour of a water system for heating Fireplace and air cooling. This was to minimise the scope of pass-throughs in water-tight bulkheads but like many design decisions this had further consequences. It made an integrated ventilation/humidification system impossible.oven provide central and space heat

The alternative to running fairly large air vents the length of the boat is local ventilation in the main zones of the boat. This is far from ideal. In both summer Central furnace and winter the air intakes will be working against the air conditioning and heating systems, respectively, and deck-mounted dorades for intake and return air are multiple hull openings. The ventilation distribution system must be designed carefully to minimise these risks of water entering.fail:

Humidity control is also difficult with local ventilation; although it may be possible to incorporate small electronic dehumidifiers into the vents. Electronic dehumidifiers use small peltier heat pumps but consume a fair bit of electrical energy. For small vents, mechanical dehumidifiers don’t scale down, Fireplace and desiccated dehumidifiers are overly complex.oven provide space heat

Standards for For heating, ventilation differ, and have varied over time subject to lobbyingair-conditioning distribution and control purposes, energy efficiency doctrines and the emergence of sick building syndrome. A reasonable yardstick boat is somewhere divided into the zones in the range of 0below table.5-With a K=1(see [[HeatingCalculation|Heating Calculation)]], the boat requires approx.25 ACH or37, more precisely, 1.0 ACH translating to around 1.66 CFM per 100 cubic feet 810 BTU/h of cabin volumeheating. You can double check The main diesel furnace supplies this to ensure at least 15 CFM/p, sufficient for the coldest weather.

For example, assume a boat having 6,000 cubic feet of volume and berths for five people. Using <table width="80%" border="1.0 ACH this yields 99.6 CFM and 15 CFM/p yields 75 CFM.">

Maximum air velocity in ventilation ducts and vents should not exceed 2.6-3.3 ft<tr><th colspan="5">HVAC Zones</s (0.8-1.0 mth></s) to minimise noise and differentials in air pressure. Air ducts for combustion systems can run as high as 40-66 ft/s (12-20 m/s).tr>

Let’s work a complete example. Assume a salon of 1280 cubic feet. At <tr> <th>Description</th> <th>Zone</th> <th>Distribution</th> <th>Air<br> Conditioning<br>BTU (K=1.0 ACH this requires 21.3 CFM:)</th> <th>Heating<br>BTU (K=1)</th></tr>

CFM = Volume * ACH<tr> <td>Forward cabin</60 minutestd> <td>1</td> <td>44% </td> <td>24,349</td ><td>16,637</td></tr>

The corresponding vent area with a velocity of <tr> <td>Aft cabin</td> <td>2 ft</td> <td>17%</td> <td>9,408</td> <td>6,428</td></s is:tr>

Vent Area = CFM<tr> <td>Pilothouse</(Velocity * 60 seconds)td>= 21. <td>3</120td>= 0. <td>18 sq ft%</td>= 25 <td>9.961</td> <td>6 sq in,806</td></tr>

In this case, we could put a <tr> <td>Engine room</td> <td>5</td> <td>- x 5</td> <td>-in intake vent at one end of the salon and a vent of the same size at the other end with an exhaust fan driving 2 ft</td> <td>?</td></tr></s.table>

== Air Conditioning ==A water-based chiller provides air conditioning. The chiller circulates chilled water through a water distribution system to But what happens in an emergency? In the cabinsevent the furnace fails, to cool them the Bristol Pacific model diesel stove in summer. All pipes should be insulated the galley can provide 6,500-16,250 BTU to prevent condensationheat the forward accommodation. (Similarly, if you opt for forced airAt the lower heat setting it could maintain a temperature differential of 21 °C, while the higher one maintains the design differential requirement of 55 °C in the ducts should be insulatedforward compartment.)

The heat exchanger can be water-air or water-At the lower setting, waterpipes, etc. A water-air exchanger would have , are protected down to work against -20 °C, a not infrequent winter temperature, which is why the design requirement is the higher 55 °C differential. Because the galley stove alone cannot heat the whole boat in the engine room, so it makes more sense to use event of a water-water furnace failure, additional heat exchanger with a keel cooler has to be supplied by the diesel fireplace in the salon. A fireplace such as a heat sinkthe Bubble produces only 3. This is overall more efficient 5 kW (the temperature differential is higher with water11,946 BTU), and avoids generating extra good for a 17 °C differential overall. So it will only heat in the engine roompilothouse and salon, not the aft cabin.

Additional cooling for one zone is provided by Therefore in an emergency in the Glacier Bay cold-plate refrigeration system [8]. coldest weather we have a heating shortfall of 21,560 BTU (A high-efficiency 12-VDC old-plate design was chosen for 6 kW). This is not critical above deck in the refrigeration to reduce AC loadssalon and pilothouse, while not imposing a continuous DC loadsince there are no water pipes there. Excess capacity may be used for air conditioningBut it is critical in the aft head.)

Calculating air conditioning is more complex Finally, some heating has to be provided to the engine room to keep water tanks and so pipes from freezing. Obviously some further development is required in the answers are more varieddesign of the back-up heating. The next table gives three sets Increasing the output of estimates the diesel stove is not a good option, as this would tend to illustrate make it less useful as a cook stove. Perhaps the issueBubble should be re-located to the aft cabin, but this negates its lifestyle purpose. More practical solutions are to shut off the water to the aft head and run the engine to keep the engine room warm. Another solution is to have an aft engineroom and a contiguous forward accommodation space.

This spreadsheet calculator is adapted from Air Conditioning Your Home [3[VentilationCalculation|Calculating Ventilation Requirements]], published by the Energy Office of Natural Resources Canada (NRCAN) and available from its web site. It appears to fall within the general range of the other methods, based on area alone. Most rules of thumb are designed for single rooms, or two rooms joined. The author's calculator considers numerous more factors:

== Related Systems == === Hot Water ===Hot water is heated in several ways. In port in summer, the water is heated by standard electrical elements operating off the AC. In winter, it is heated by the water jacket on the diesel oven. If the oven is not in use, and there is no other source of heat, the hot water tank defaults to the electrical elements. Under way, engine coolant circulates through the hot water tank, and hence to a water-water heat exchanger with keel cooler. Another feature of this design is that raw seawater is not circulated through the engine. There is a bypass circuit around the water heater that closes thermostatically when the heater is at temperature. (The next article will describe a tankless design for a hot-water heater with a solar collector and engine pre-heat.) In winter if the boat is out of the water, the engine may have to be run to charge the batteries. In this case, an optional water-air radiator in the engine room provides engine cooling. Use an anti-scald, balanced-pressure shower valve (not a tempering valve!) on the showers to regulate the water to 120 F. This will avoid scalding people, and reduce water consumption. Bathers will be able to mix the water faster to a comfortable temperature. === Watermaker ===For cold water expeditions, the water intake to the watermaker should be preheated. === Engine Cooling === === Refrigeration === == [[Category:HVAC Scenarios ==]]